"It made me wonder how often it happens that someone has some metal in their body, but they’re not aware of it. What happens then? Are any security systems built in the process to detect this before someone has a tiny bit of metal ripped out of their skull?"
It happens from time to time, but very rarely that one of the screening questions doesn't trigger a memory. If you just ask "do you have any metal in you?" you might miss a lot, but when you go through the various ways people can get metal in them and ask "have you ever had a stent put in? Have you ever been in a war zone or had a shrapnel injury? Do you have an artificial joint?" you tend to pick up on the risks.
There are ~150 adverse events/year in the US for MRIs, but the vast majority of those are thermal, with some external projectiles. Metal doesn't typically get pulled out of peoples' bodies even in the accidents -- most metal that's magnetic enough to do that isn't biocompatible in the first place, and in the very rare case where someone passes the screening question with unknown metal and goes in, they might feel it try to move as they get close and back off. Aneurysm clips and vascular stents are the biggest concern from what I recall (tiny movements or heating can have very bad outcomes), but medical device manufacturers have been making most of them (all?) MRI-compatible for the last 20+ years.
Most implanted bits of metal are not a safety risk, but screw up the images. Dental work, for instance, leaves the area around the jaw just a black void. Or they are conductive but not magnetic, so they don't get moved around but can heat up (those thermal AEs). The most common source of unknown metal/conductive material is bad tattoos.
Every now and then a company tries to pitch a metal detector for MRI suites, but they don't work well enough to bother with. The questionnaire and the metal macarana are the security systems.
Wild to think that in the US most AC/heat-pump units are for cooling, whereas in the UK heat pumps are almost exclusively for heating. I wonder if this is also true for areas of the US where heating demand is equal to cooling?
"It made me wonder how often it happens that someone has some metal in their body, but they’re not aware of it. What happens then? Are any security systems built in the process to detect this before someone has a tiny bit of metal ripped out of their skull?"
It happens from time to time, but very rarely that one of the screening questions doesn't trigger a memory. If you just ask "do you have any metal in you?" you might miss a lot, but when you go through the various ways people can get metal in them and ask "have you ever had a stent put in? Have you ever been in a war zone or had a shrapnel injury? Do you have an artificial joint?" you tend to pick up on the risks.
There are ~150 adverse events/year in the US for MRIs, but the vast majority of those are thermal, with some external projectiles. Metal doesn't typically get pulled out of peoples' bodies even in the accidents -- most metal that's magnetic enough to do that isn't biocompatible in the first place, and in the very rare case where someone passes the screening question with unknown metal and goes in, they might feel it try to move as they get close and back off. Aneurysm clips and vascular stents are the biggest concern from what I recall (tiny movements or heating can have very bad outcomes), but medical device manufacturers have been making most of them (all?) MRI-compatible for the last 20+ years.
Most implanted bits of metal are not a safety risk, but screw up the images. Dental work, for instance, leaves the area around the jaw just a black void. Or they are conductive but not magnetic, so they don't get moved around but can heat up (those thermal AEs). The most common source of unknown metal/conductive material is bad tattoos.
Every now and then a company tries to pitch a metal detector for MRI suites, but they don't work well enough to bother with. The questionnaire and the metal macarana are the security systems.
Wild to think that in the US most AC/heat-pump units are for cooling, whereas in the UK heat pumps are almost exclusively for heating. I wonder if this is also true for areas of the US where heating demand is equal to cooling?